The first motorized vehicles had little in the way of an electrical system. All that was required was some way to generate and distribute an ignition potential to each of the cylinders of the small, internal combustion engine that powered these early vehicles.
The need to see the road ahead during nighttime operation gave rise to the first electrical accessory: headlights. Interior illumination was added for the operator's convenience, and a single tail light was considered adequate. Turn signal lights followed, but the simple vehicle radio receiver did not make its appearance until a number of years later.
The modern automobile is an impressive collection of electrical hardware: from stereo sound equipment to air conditioning; from power windows, mirrors and seats to keyless entry systems; from vehicle alarms to seat position memory to electrically heated seats. The complexity of vehicle electrical systems has grown almost exponentially since the automobile's introduction.
An automotive electrical system is a formidable combination of high-current and low-current circuitry. In many cases, relays are required for control purposes, and all circuits must be adequately fused to protect expensive components and to guard against the danger of fire. In order to facilitate the replacement of fuses and relays, and to simplify interconnection of electrical hardware, many different electric power distribution systems have been tried.
One approach that has been tried with fair consistency is to centralize fuse and relay mounting, then route input and output connections from this central location. The first systems built using this approach included a great deal of point-to-point wiring. Hand wiring is very costly, and manual wiring operations are a source of wiring errors that negatively impact product quality.
Another approach has been the construction of customized distribution networks stamped from thin metal sheets. These stampings are then contorted so that contact tabs protrude through openings in custom designed plastic shells. Although this approach yields a higher quality product, tooling costs are very high, since virtually every automobile model requires a unique distribution system. At least some of this uniqueness aspect is driven by the proliferation of fuse and relay packages. A distribution product must be able to accommodate the fuse and relay components selected by the manufacturer.
Yet another approach has centered around the use of flexible circuit board technology, or "flex circuits." Flex circuits are constructed by depositing conductive material between two flexible insulating layers. Although the unique distribution requirements of each vehicle model would require unique flex circuits for each application, tooling costs are much lower than the metal stamping/custom plastic housing approach described previously. The principal disadvantage of the flex circuit approach is that the conductive layers are very thin, and the high current densities required in vehicle power distribution lead to overheating and eventual failure.
Consequently, a need arises for a vehicle electric power distribution system that can be customized for a particular vehicle with relative ease, that avoids high tooling costs for custom designed components, that is reliable in a high current environment, that will accommodate a wide range of fuse and relay packages, and that is relatively inexpensive to manufacture.